1. Field of the Invention
This invention concerns an alarm device for liquid level changes in general. More specifically, it deals with an apparatus that is particularly adaptable for use in residential dwelling sewer systems.
2. Description of the Prior Art
Heretofore, there have been various proposals for providing means to signal an alarm when the fluid level in a sewer system backs up. However, all such known devices have had various drawbacks. For example, there is a U.S. Pat. No. 3,757,316, which has a sensing device in the form of a pair of electrodes that are immersed in the fluid when the level rises to a certain height. The change in conductivity is measured and therefore this depends upon a relatively sensitive change. Furthermore, these electrodes would be subject to corrosion, and in addition they subject the sewage fluids to whatever electrical signals exist on the electrodes.
Another prior device is shown by U.S. Pat. No. 3,774,187. It discloses a float supported by a vertical rod that makes sliding movement through its guides in order to close an electrical contact at the top of the rod when the fluid rises. This arrangement is clearly subject to sticking with corrosion from nonuse, and it employes a point contact switch which would be very unreliable.
Consequently, it is an object of this invention to provide a simple, yet highly reliable system that will indicate the potential backup of sewage in a residential sewage drain.